1. Field of the Invention
The present invention relates generally to electrical connectors. More particularly, the present invention relates to a method of and system for interconnecting a printed circuit board to the rear of an electrical socket or plug.
2. Description of the Prior Art
Present methods of and systems for terminating a printed circuit board to the rear of an electrical socket or plug connector include soldering the connector contact tails to the board. The purpose of the soldering operation is to provide electrical and mechanical connection. In some instances, the heat generated by the soldering process can adversely effect the connector and printed circuit board. As a result, the electrical performance of the interconnect can be irreparably destroyed or, at the least, significantly degraded. Performance degradation, of course, must be avoided in electronics devices that are used in avionics and other sensitive systems, especially where rigid specifications must be met.
Moreover, soldering can create a rigid connection between the components. When a member soldered to a printed circuit board is deformed due to tensile, compressive or torque forces acting on the member, those forces can be propagated or transferred into the substrate of the printed circuit board causing internal stress. The stress can then damage the substrate or the crystal lattice structure associated with the circuits on the printed circuit board resulting in damage to the device.
The present method solves the problems associated with soldering and rigid connections by providing an interconnect between a socket and a printed circuit board whereby the means for attaching the two components together is made without soldering or using other methods involving heat. Moreover, the present invention solves that problem without introducing new problems, such as causing internal stresses in the printed circuit board that can also result in performance degradation.
Solderless interconnects are not new. U.S. Pat. No. 4,799,904 to Sutcliffe, for example, discloses a cylindrical connector contact for an electrical socket that can be mated to a printed circuit board. The contact, like in the present invention, provides the means for attaching the socket to the printed circuit board. The contact is made of a conducting material so that there is electrical continuity between an electrical conductor inserted in the front end of the contact and the circuits on the printed circuit board. In Sutfliffe, the contact has a plurality of axially spaced “barbs” arranged in a purely circumferential direction on the distal or “tail” portion of the contact. Those barbs engage rings on the wall of a circuit board through hole thereby retaining the contact within the hole. The larger the diameter of the hole, the greater the number of rings and barbs that are needed to ensure adequate mechanical attachment. Sutcliffe teaches that at least two barbs and rings are required to achieve a stable electrical contact. To allow for dimensional tolerances to be relaxed, the tail includes an axial cut so that the tail portion becomes flexible, which could reduce internal stresses on the printed circuit board at the connection point.
There are several problems associated with the contact disclosed in Sutcliffe. First, it is difficult and expensive to manufacture barbs and rings with tolerances in the order of a few hundredths of an inch. Moreover, if the contact is inserted in the printed circuit board through hole too far, only one barb and ring may make contact, reducing the electrical continuity between the two components and also lowering the mechanical forces retaining the contact in the hole. Further, only a portion of barb actually makes contact with a ring inside the hole, which limits the amount of electricity that can be conducted between the two parts.
U.S. Pat. No. 4,374,607 to Bright et al. also discloses an interconnect that does not require soldering but, unlike Sutcliffe, uses axially spaced “undercuts” or teeth on the distal or tail portion of a pin contact to mate with corresponding axially spaced grooves on a socket. When inserted, the undercuts engage and retain the contact in the socket.
The problem with the pin contact disclosed in Bright et al. is that electrical conductivity is made at the very distal end of the contact, which would not be feasible if it were used to conduct electricity to a printed circuit board. Pin contacts used for printed circuit boards generally require electrical contact at or near the same point where mechanical attachment occurs. That type of connection is preferred in many cases because the tensile and compressive forces transmitted through the contact to the printed circuit board must be minimized, as noted above, to reduce internal stresses on the board. Internal stresses can damage the crystal structure of, for example, the logic circuits on the board and cause circuit failure.
U.S. Pat. No. 4,701,004 to Yohn discloses a solderless cylindrical retention clip for receiving an electrical contact pin of an electrical connector. The clip is inserted inside a bore hole. One end of the clip includes two cantilevered springs or lances projecting radially inward toward the longitudinal axis of the clip. The ends of the springs engage a shoulder or groove formed on a pin. The shoulder extends perpendicular to the longitudinal axis of the pin (i.e., radially).
One obvious problem with the retention clip disclosed in Yohn is that it is not designed to conduct electricity. So while a contact inserted in the clip is retained and prevented from moving in a direction longitudinal to the contact axis, no electrical signals are conducted through the clip to another system.
U.S. Pat. No. 4,050,772 to Birnholz et al. discloses a contact pin and printed circuit board through hole receptacle for receiving the contact and conducting electricity. The through hole receptacle includes a rectangular lip around the opening of the hole and an annular electrical contact surrounding the opening of the hole. Together, those components engage the rear shoulder of a flange at the top of a contact pin as it is inserted in the hole. Another portion of the through hole inside the hole engages a radially-extending shoulder of a barb on the shank of the contact.
The problem with the contact pin disclosed in Birnholz et al. is that the rigid metal barb of the contact forces the plastic hole apart during insertion of the contact. That can cause internal stresses within the printed circuit board in the vicinity of the through hole that can damage the performance of the device. Also, the contact through hole receptacle forms a rigid connection with the contact, which is disadvantageous in some applications as noted previously.
The various approaches described in the above-cited patents for making solderless interconnects have not been found to be totally satisfactory solutions. This is especially true in the context of electrical interconnects used in highly demanding applications like aircraft connectors.